Discharge lamps, dosed with special radiating materials such as metal halides, are among the most efficient light sources mankind has ever made. Combined with high lumens output and excellent color balance, these light sources are used in general lighting illuminating buildings, streets, large facilities as well as special applications such as projectors and automobiles. Though the lamps have been engineered so that the majority of the radiation is in the visible range, which contributes to the high lumen efficacy, there is a significant portion of UV radiation that has to be filtered out. The filtering can be carried out by the fixture itself or by using an additional optical element; a light source without UV radiation would increase the usage of the light source and reduce the adverse impact of the UV radiation to the fixture materials.
TiO2 is a common oxide that has widespread applications. Due to its wide band gap at around 3 eV, TiO2 is effective in absorbing ultraviolet (UV) radiation that enables many UV-blocking applications. TiO2 also possesses strong photo-catalytic effect; that is when it is irradiated by UV radiation, it produces OH and O radicals on the surface that are potent in breaking down dusty materials and destroying microbiological agents, inspiring self-cleaning and germicidal applications.
Flow-limited field-injection electrostatic spraying (FFESS) is a novel thin-film deposition method wherein field-injection charging using a nano-sharpened tungsten electrode inserted in an insulating nozzle produces electrostatic spray of precursor solutions. These charged nano-drops are subsequently accelerated toward a substrate (room-temperature or heated) for film deposition showing many advantages for the fabrication of thin films: (a) the electrostatic repulsion between the charged nanodrops delivered onto the substrate helps to produce homogeneous coating; (b) the very large specific surface area of the nanodrops makes the film deposition highly receptive to pyrolysis and annealing; (c) no vacuum is required for the deposition; (d) even relatively insulating solutions can be sprayed successfully because of the field-injected charge; (e) since field injection can generate high currents at low applied voltages giving rise to a high and uniform surface-charge density, multiple-jet sprays can be generated in a stable and reproducible manner giving more uniformity to spray distribution.